The objective of this research program is to further our understanding of how genetic, environmental, and physiological variables act and interact to produce differences in behavior. The current proposal is concerned primarily with the effects of these variables on "sex-drive" in male house-mice and in masculinized female house-mice. Specifically, the proposed studies involve: (1) Artificial selection for high and low sex-drive. (2) A diallelic genetic analysis of retention of the ejaculatory reflex after castration. This experiment tests the hypothesis that relatively few genes account for genotypic differences in post-castration sexual behavior. (3) Investigation of the causes of the temporary four-fold increase in mating time in the first two months following castration. (4) A test of the hypothesis that there is a short-lived (two day) decrease in mating-time immediately following castration. (5) Experiments on the masculine behavior pattern of females injected with testosterone propionate on the day of birth. Involved are dose-response studies, investigation of strain differences, and the development of sexual behavior in the masculinized females. (6) An attempt to isolate protein differences in tissue from the preoptic hypothalamic area of castrated and noncastrated mice using polyacrylamide gel electrophoresis and the immunological response in rabbits. (7) An attempt to measure serum testosterone levels by gas chromatography and to correlate differences with behavioral differences.